TREATMENT OF TEXTILE DESIZING WASTE-WATER BY PILOT-SCALE NANOFILTRATION MEMBRANE SEPARATION

Desizing wastewaters from the bleaching and dyeing industry of Hong Ko ng were treated by nanofiltration (NF) membrane separation on a pilot scale in the pressure controlled region. The two brown colored wastewa ters had chemical oxygen demand (GOD) of 14,000 mg 1(-1) and 5430 mg 1 (-1), respectively. Permeate flux and COD retention were investigated in relation to transmembrane pressure drop, temperature, and feed-solu tion concentration. The permeate flux was found to increase significan tly with transmembrane pressure drop and to decrease with feed concent ration. Higher permeate flux was found for wastewater with higher pH. A minor increase in COD retention was found for the increase in transm embrane pressure drop as well as operating temperature. The COD retent ion was about 95% for wastewater with pH 10.2, and 80-85% for wastewat er with pH 5.5. The difference in the results obtained for the two kin ds of wastewater was attributed to their compositional difference that resulted from the desizing operation. Fouling of membrane is not a bi g concern for the NF membrane tested in treating this type of wastewat er. The quality of the permeate is all above the discharge standard fo r foul sewer in Hong Kong. The experimental results are consistent wit h the theoretical analysis.